Tensioner with spring damper

ABSTRACT

A tensioner having a closing-type torsion spring that is employed to bias a pivot arm about a pivot shaft. The tensioner includes a damper that continuously contacts an inside surface of the torsion spring to dampen torsional vibration transmitted through the torsion spring.

INTRODUCTION

The present disclosure generally relates to a tensioner with a springdamper.

U.S. Pat. No. 7,507,172 discloses a tensioner that employs a frictionbrake. While such tensioners are satisfactory for their intended uses,we note that such tensioners are nonetheless susceptible to improvement.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present teachings provide a tensioner that includes apivot shaft, a pivot arm, a torsion spring and a damper. The pivot armis pivotally mounted on the pivot shaft. The torsion spring biases thepivot arm about the pivot shaft in a first rotational direction. Thetorsion spring is a closing-type torsion spring with a plurality ofcoils that are received about the pivot shaft. The damper is disposed incontinuous contact with an inside surface of the coils of the torsionspring. The damper includes a resilient member that deflects radiallyinwardly in response to contact with the coils of the torsion spring.

In another form, the present teachings provide a tensioner having apivot shaft, a pivot arm, a torsion spring, a stop sleeve, a first clampsleeve, a wrap spring, a second clamp sleeve, at least one damper and afriction clamp. The pivot arm is pivotally mounted on the pivot shaftand defines a groove. The torsion spring biases the pivot arm about thepivot shaft in a first rotational direction. The torsion spring is aclosing-type torsion spring with a plurality of coils that are receivedabout the pivot shaft. The stop sleeve is received over the pivot shaftand within the torsion spring. The stop sleeve has a tongue that isreceived into the groove in the pivot arm. The tongue is smaller thanthe groove to permit a predetermined amount of movement of the pivot armrelative to the stop sleeve. The first clamp sleeve is mounted over thepivot shaft and is rotatably coupled to the stop sleeve. The wrap springhas a first end, which is fixedly coupled to the first clamp sleeve, anda plurality of helical coils that are disposed about the stop sleeve.The second clamp sleeve is mounted over the pivot shaft and abuts thefirst clamp sleeve on a side opposite the stop sleeve. The second clampsleeve is non-rotatably coupled to the first clamp sleeve. The at leastone damper is coupled to the second clamp sleeve and is configured to bein continuous contact with an inside surface of the coils of the torsionspring. The at least one damper is formed of a resilient material anddeflects inwardly with increasing torque transmitted through the torsionspring. The friction clamp is housed between the first and second clampsleeves and frictionally engaging the pivot shaft.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.Similar or identical elements are given consistent identifying numeralsthroughout the various figures.

FIG. 1 is a schematic illustration of an exemplary tensioner constructedin accordance with the teachings of the present disclosure shown inoperative association with the timing drive of an engine;

FIG. 2 is an exploded perspective view of the tensioner of FIG. 1;

FIG. 3 is a section view of the tensioner of FIG. 1 taken longitudinallythrough the pivot shaft;

FIG. 4 is a top perspective view of a portion of the tensioner of FIG.1, illustrating the backstop device in more detail;

FIG. 5 is a bottom view of a portion of the backstop device,illustrating the first clamp sleeve in more detail;

FIG. 6 is a top plan view of a portion of the backstop deviceillustrating the second clamp sleeve in more detail

FIG. 7 is a perspective view of the second clamp sleeve;

FIG. 8 is a bottom perspective view of the backstop device;

FIG. 9 is a partly sectioned view of the tensioner of FIG. 1illustrating the main spring contacting the damping members;

FIG. 10 is a bottom view of another second clamp sleeve constructed inaccordance with the teachings of the present disclosure; and

FIGS. 11 through 13 are perspective views of other second clamp sleevesconstructed in accordance with the teachings of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

With reference to FIG. 1, a tensioner constructed in accordance with theteachings of the present disclosure is generally indicated by referencenumeral 10 and operatively associated with an engine 12. The engine 12can include a timing drive 14 in which an endless power transmittingelement 16, such as a toothed belt, drivingly couples a driving sprocket18, which can be coupled to a source of rotary power, such as acrankshaft 20, and a driven sprocket 22, which can be coupled to adriven device, such as a camshaft 24, and the tensioner 10 is employedto apply and maintain a tensioning force on the endless powertransmitting element 16. Except as specifically noted herein, thetensioner 10 may be similar to the tensioner that is described in U.S.Pat. No. 7,507,172, the disclosure of which is hereby incorporated byreference as if fully set forth in detail herein.

With additional reference to FIG. 2, the tensioner 10 can include apulley assembly 40, a pivot arm 42, a pivot shaft 44, a thrust washer46, a base plate 48, a main spring 50, and a backstop device 52.

With reference to FIGS. 2 and 3, the pulley assembly 40 can include apulley 60 and a bearing 62. In the particular example provided, thepulley 60 is configured to engage a rear, untoothed side of the endlesspower transmitting element 16 (FIG. 1), but it will be appreciated thatpulley 60 could be configured with teeth or other features as desired,depending on the particular type of endless power transmitting elementthat is employed in the timing drive 14 (FIG. 1), as well as theparticular side and/or location in which the pulley 60 engages theendless power transmitting element employed in the timing drive 14 (FIG.1). The bearing 62 can be fixedly coupled to the pulley 60 and can beemployed to support the pulley 60 for rotation on the pivot arm 42 abouta first axis 66. In the particular example provided, the outer bearingrace of the bearing 62 is integrally formed with the pulley 60.

The pivot shaft 44 can be employed to pivotally mount the pivot arm 42to a structure of the engine 12, e.g., an engine block or cover, forrotation about a second axis 68 that can be parallel to but offset fromthe first axis 66. In this regard, the pivot shaft 44 can be generallyhollow so as to receive a threaded fastener T that can fixedly couplethe pivot shaft 44 to the engine 12. In the particular example provided,the pivot shaft 44 includes a head 70, a body portion 72 and anecked-down portion 74 that is coupled to an end of the body portion 72opposite the head 70.

The thrust washer 46 can be mounted on the pivot shaft 44 between thehead 70 and the pivot arm 42 and can be configured to control thefriction between the pivot shaft 44 and the pivot arm 42 when the pivotarm 42 rotates relative to the pivot shaft 44. In the particular exampleprovided, the thrust washer 46 is formed of nylon 4/6 with aramid fiberreinforcement. The thrust washer 46 can overlie the bearing 62 to shieldthe bearing 62 from dust, dirt and moisture.

The base plate 48 can comprise a container-like structure having anannular side wall 90 and a rear wall 92 that can be fixedly coupled tothe pivot shaft 44. In the particular example provided, the base plate48 comprises an inner collar 96 that is fixedly coupled in anappropriate manner, such as an interference fit, to the necked-downportion 74 of the pivot shaft 44. A locating member 98, such as arearwardly extending tang, can be coupled to or formed on the base plate48 and can be employed to orient the tensioner 10 in a predeterminedorientation relative to the engine 12.

The main spring 50 can be disposed between the pivot arm 42 and the baseplate 48 and can bias the pivot arm 42 in a predetermined firstrotational direction relative to the base plate 48. The main spring 50can be any type of torsion spring but in the particular exampleprovided, the main spring 50 is a closing-type spring (i.e., a helicalcoil spring that coils more tightly with increasing torque) that isformed of round wire. The main spring 50 can include a first tang 100,which is received into an aperture 102 formed in the pivot arm 42, and asecond tang 104 that is received into an aperture 106 formed in the baseplate 48 (note that the first and second tangs 100 and 104 and theapertures 102 and 106 have been illustrated out of position in FIG. 3for purposes of clarity). It should be appreciated, however, that themain spring 50 could be an opening-type spring and/or if desired, themain spring 50 could be formed of a square or rectangular wire.

The backstop device 52 can include a friction clamp 120, a first clampsleeve 122, a stop sleeve 124, a clutch spring 126, and a second clampsleeve 128.

With reference to FIGS. 3 and 5, the friction clamp 120 can beconfigured similar to an external snap ring and can be configured tofrictionally engage the pivot shaft 44. In the particular exampleprovided, the friction clamp 120 is configured to make contact with aportion of the circumference of the necked-down portion 74 of the pivotshaft 44. The friction clamp 120 can be made of any appropriatematerial, such as an uncoated stainless steel spring wire having asquare 3 mm by 3 mm cross-sectional area, but it will be appreciatedthat various other materials (including coatings) and material sizes maybe employed to suit a particular application of the tensioner 10.

With reference to FIGS. 3 through 5, the first clamp sleeve 122 cancomprise an annular body 140, an annular peripheral wall 142, aplurality of flexural fingers 144, and a plurality of tenons 146 a, 146b and 146 c. The annular body 140 can define an abutting surface 150, apivot shaft aperture 152 and an inwardly extending lip member 154. Theabutting surface 150 can be configured to abut an upper side of thefriction clamp 120. The pivot shaft aperture 152 can be configured toreceive the body portion 72 of the pivot shaft 44, while the lip member154 can be configured to abut a shoulder 160 on the pivot shaft 44 atthe transition between the body portion 72 and the necked-down portion74. The peripheral wall 142 can be contoured to envelope the outerperimeter of the friction clamp 120. In the example provided, theperipheral wall 142 defines a first end groove 170, which is configuredto hold a first end 172 of the friction clamp 120, and a second endgroove 174 which is configured to retain a second end 176 of thefriction clamp 120. The first end groove 170 can be constructed in anarrow manner that inhibits relative rotation between the first end 172of the friction clamp 120 and the first clamp sleeve 122, whereas thesecond end groove 174 can be constructed somewhat wider so as to permitrelative rotation of the second end 176 of the friction clamp 120 in amanner that spreads the friction clamp 120. Also, the size of the secondend groove 174 can be selected to compensate for the manufacturingvariance in the friction clamp 120 (including the positioning of thefirst and second ends 172 and 176 of the friction clamp 120.) and in thediameter of the necked-down portion 74 of the pivot shaft 44.Construction in this manner permits the first and second ends 172 and176 of the friction clamp 120 to be maintained in a predeterminedposition relative to one another or to further close the friction clamp120 about the pivot shaft 44 to maintain or close the shape of thefriction clamp 120 to thereby maintain or increase the friction forcebetween the friction clamp 120 and the pivot shaft 44 when the firstclamp sleeve 122 is rotated in the first rotational direction. It willbe appreciated that the friction force applied by the friction clamp 120is ordinarily sufficient to inhibit movement of the first clamp sleeve122 about the pivot shaft in the first rotational direction.Configuration in this manner also permits the first and second ends 172and 176 of the friction clamp 120 to be spread apart from one another(thereby opening the shape of the friction clamp 120 to decrease thefriction force between the friction clamp 120 and the pivot shaft 44)when a torque in excess of a predetermined torque is applied to thefirst clamp sleeve 122 in a second rotational direction (opposite thefirst rotational direction). It will be appreciated that the frictionforce applied by the friction clamp 120 can prevent rotation of thefirst clamp sleeve 122 relative to the pivot shaft 44 when the torqueapplied to the first clamp sleeve 122 is less than or equal to thepredetermined torque and that application of a torque exceeding thepredetermined torque may be appropriate in instances where the pivot arm42 is moved manually to replace an endless power transmitting element.The flexural fingers 144 can be coupled to and spaced circumferentiallyabout the annular body 140 on a side opposite the peripheral wall 142.The flexural fingers 144 can extend axially from the annular body 140 soas to be cantilevered therefrom and can comprise a retaining tab 180that is configured to engage the stop sleeve 124 as will be described ingreater detail, below. The tenons 146 a, 146 b and 146 c can extendaxially from the peripheral wall 142. An axially extending hole 184 canbe formed through a first one of the tenons 146 a.

With reference to FIGS. 3 and 4, the stop sleeve 124 can include anannular sleeve body 200, a circumferentially extending external rimmember 202, a tongue 204 and a circumferentially extending internal rimmember 206. The sleeve body 200 can define an internal aperture 210 thatcan be sized to receive an annular shoulder 212 formed on the pivot arm42, as well as the flexural fingers 144 of the first clamp sleeve 122.The external rim member 202 can be coupled to an upper end of the sleevebody 200 and can extend radially outwardly therefrom. The tongue 204 canextend axially upwardly from the external rim member 202 and can beconfigured to engage a tongue cavity 216 formed in the pivot arm 42. Itwill be appreciated that the tongue 204 can have a cross-section (takenperpendicular to the longitudinal axis of the pivot shaft 44) that canbe shaped as a circular ring sector that is defined by a first includedangle, and that the tongue cavity 216 can have a similar cross-sectionalshape that is defined by a second included angle that is greater thanthe first included angle such that the pivot arm 42 can pivot to alimited extent about the pivot shaft 44 without contacting the stopsleeve 124 (so as not to effect operation of a clutch that is formed bythe friction clamp 120, the first clamp sleeve 122, the stop sleeve 124and the clutch spring 126). The internal rim member 206 is configured tobe engaged by the retaining tab 180 of the flexural fingers 144 toinhibit separation of the stop sleeve 124 from the first clamp sleeve122 in an axial direction.

With reference to FIGS. 3 through 5, the clutch spring 126 can be awrap-type spring that can include a plurality of helical coils 230, atang 232, which extends from a first side of the helical coils 230, anda free end 234 that is associated with a second, opposite end of thehelical coils 230. The clutch spring 126 can be formed of any desiredmaterial, but in the particular example provided, is formed of astainless spring steel wire having rectangular cross-section having asize of about 1 mm wide by 1.5 mm tall. The tang 232 can be turned at anangle of 90° from the helical coils 230. The clutch spring 126 can bereceived over the sleeve body 200 of the stop sleeve 124 such that thefree end 234 abuts the external rim member 202. The helical coils 230can be wound in a direction or sense that is opposite the direction orsense in which the main spring 50 is wound. The tang 232 can be receivedin the axially extending hole 184 in the tenon 146 a of the first clampsleeve 122. It will be appreciated that the tang 232 can be insertedinto the axially extending hole 184 when the first clamp sleeve 122 isinstalled to the stop sleeve 124.

As assembled to the first clamp sleeve 122 and the clutch spring 126,the stop sleeve 124 is able to rotate about the flexural fingers 144(and the pivot shaft 44) in the first rotational direction, but not inthe second rotational direction due to the configuration of the clutchspring 126. More specifically, the clutch spring 126 tends to uncoilfrom the sleeve body 200 and thereby disengage the stop sleeve 124 whenthe stop sleeve 124 is subjected to a force that would tend to rotatethe stop sleeve 124 in the first rotational direction, but tends to coilmore tightly around the sleeve body 200 and thereby grippingly engagethe stop sleeve 124 when the stop sleeve 124 is subjected to a forcethat would tend to rotate the stop sleeve 124 in the second rotationaldirection. Accordingly, it will be appreciated that the friction clamp120, the stop sleeve 124, the first clamp sleeve 122 and the clutchspring 126 cooperate to form a one-way clutch that permits the stopsleeve 124 to rotate relative to the first clamp sleeve 122 in the firstrotational direction, but inhibits rotation of the stop sleeve 124relative to the first clamp sleeve 122 in the second rotationaldirection. It will be appreciated, however, that while the particulartensioner 10 has been described and illustrated with a one-way clutch,the teachings of the present disclosure have broader applicability andas such, the presence of a one-way clutch in a tensioner constructed inaccordance with the present disclosure is entirely optional. Forexample, the friction clamp 120, the first clamp sleeve 122, the secondclamp sleeve 124 and the clutch spring 126 could be eliminated in theirentirety from the tensioner 10 if a one-way clutch is not desired.

With reference to FIGS. 3, and 6 through 8, the second clamp sleeve 128can comprise an annular end wall 250, a plurality of spring limiters 252and a side wall 254. The second clamp sleeve 128 can be unitarily formed(e.g., injection molded) from a suitable material, such as nylon 4/6 ornylon 4/6 with aramid fiber reinforcement. The second clamp sleeve 128can be non-rotatably coupled to the first clamp sleeve 122, and thefriction clamp 120 can be received into the interior of the second clampsleeve 128.

The end wall 250 can be abutted against an interior surface of the rearwall 92 of the base plate 48 and can be disposed over the necked-downportion 74 of the pivot shaft 44. An opposite axial side of the end wall250 can abut the friction clamp 120 on a side opposite the abuttingsurface 150. A plurality of apertures 260 can be formed into the endwall 250 to receive the tenons 146 a, 146 b and 146 c to thereby couplethe first clamp sleeve 122 to the second clamp sleeve 128.

The spring limiters 252 can be coupled to the end wall 250 and spacedcircumferentially about the end wall 250 at a predetermined distancefrom the clutch spring 126 and can be configured to limit radial outwardexpansion of the clutch spring 126 to a predetermined dimension. In theparticular example provided, two spring limiters 252 are employed, witheach spring limiter being aligned radially with an associated one of thetenons 146 b and 146 c. It will be appreciated, however, that more orfewer spring limiters 252 could be employed and that their locationabout the end wall 250 could be different from that which is describedand illustrated herein.

The side wall 254 can be coupled to the annular end wall 250 and candefine a plurality of retaining members 270 and a plurality of dampingmembers 272. The retaining members 270 can be coupled to and extend fromthe end wall 250 and can define a set of projections 276 that can engagethe annular body 140 of the first clamp sleeve 122 in a snap-fit mannerthat retains the first clamp sleeve 122 to the second clamp sleeve 128.

With reference to FIGS. 3, 4 and 9, the damping members 272 can becoupled to the retaining members 270 and can be configured such that atleast one of the damping members 272 contacts the inside surface 280 ofthe main spring 50 at all times to dampen vibration that is transmittedthrough the main spring 50. The degree of contact between the dampingmembers 272 and the main spring 50 can be dictated by the degree towhich vibration in the main spring 50 is to be damped. In the particularexample provided, each of the damping members 272 comprises an annularsector 290 that is coupled on opposite ends to an adjacent pair of theretaining members 270 via a pair of end members 292 such that acircumferentially extending space 294 is disposed between the end wall250 and the annular sector 290. The annular sector 290 can be lobed,rather than circular, such that it is furthest away from a longitudinalaxis of the second clamp sleeve 128 at its mid-point.

Returning to FIGS. 3 and 9, the pivot arm 42 can rotate about the pivotshaft 44 during operation of the tensioner 10 to maintain a desiredlevel of tension in the endless power transmitting element 16 (FIG. 1).Movement of the pivot arm 42 can cause a corresponding coiling oruncoiling of the main spring 50. In some instances, the movement of thepivot arm 42 might tend to cause the main spring 50 to vibrate at aresonant frequency. The annular sectors 290 can deflect in response tocontact with the main spring 50; the friction associated with thiscontact, as well as the energy required to deflect the annular sectors290, can help attenuate vibration and prevent the main spring 50 fromentering resonance.

With reference to FIGS. 10 through 13, other second clamp sleevesconstructed in accordance with the teachings of the present disclosure.In FIG. 10, the second clamp sleeve 128 a comprises an annular side wall254 a and a single damping member 272 a having an annular sector 290 athat is coupled to the side wall 254 a by a pair of end members 292 aand an intermediate member 300.

In FIGS. 11 through 13, each of the second clamp sleeves 128 b, 128 cand 128 d comprises an annular side wall 254 b and a plurality ofdamping members 272 b that are coupled to and extend radially outwardlyfrom the side wall 254 b. In the particular examples provided, thedamping members 272 b comprise a single arcuate sector 290 b that iscoupled to the side wall 254 b via a single end member 292 b.

Accordingly, it will be appreciated that the damping members could beshaped in any appropriate manner. In this regard, the damping membersneed not be arcuate or be unitarily formed with the remainder of thesecond clamp sleeve, but could comprise one or more components that canbe assembled to or molded onto the remainder of the second clamp sleeve.For example, the spaces 294 a defined by the annular sector 290 a, theside wall 254 a, the end members 292 a and the intermediate wall 300 inFigure-could be filled with a resilient material, e.g., via overmolding,that can further stiffen the damping member 272 a where a relativelyhigher degree of damping is required. It will also be appreciated thatthe damping member (or a material that is employed to stiffen thedamping member) could be configured with multiple spring rates toprovide additional levels of damping. For example, the second clampsleeves 128 b, 128 c and 128 d could be configured such that a firstportion of the damping members 272 b have a first cross-sectional area(and therefore a first spring rate) while a second portion of thedamping members 272 b could have a second, larger cross-sectional area(and therefore a second spring rate). If multiple spring rates areemployed, the damping member can be configured to provide a first springrate when the main spring 50 deflects the damping member by an amountthat is less than or equal to a predetermined amount and a second springrate when the damping member is deflected by an amount that is greaterthan the predetermined amount.

It will be appreciated that the above description is merely exemplary innature and is not intended to limit the present disclosure, itsapplication or uses. While specific examples have been described in thespecification and illustrated in the drawings, it will be understood bythose of ordinary skill in the art that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the present disclosure as defined in the claims.Furthermore, the mixing and matching of features, elements and/orfunctions between various examples is expressly contemplated herein sothat one of ordinary skill in the art would appreciate from thisdisclosure that features, elements and/or functions of one example maybe incorporated into another example as appropriate, unless describedotherwise, above. Moreover, many modifications may be made to adapt aparticular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular examples illustrated by the drawings and described in thespecification as the best mode presently contemplated for carrying outthe teachings of the present disclosure, but that the scope of thepresent disclosure will include any embodiments falling within theforegoing description and the appended claims.

1. A tensioner comprising: a pivot shaft; a pivot arm pivotally mountedon the pivot shaft; a torsion spring that biases the pivot arm about thepivot shaft in a first rotational direction, the torsion spring being aclosing-type torsion spring with a plurality of coils that are receivedabout the pivot shaft; a damper disposed in continuous contact with aninside surface of the coils of the torsion spring, the damper comprisinga resilient member that deflects radially inwardly in response tocontact with the coils of the torsion spring, the damper being disposedin an axially stationary position relative to the pivot shaft.
 2. Thetensioner of claim 1, further comprising a one-way clutch disposedbetween the pivot shaft and the torsion spring, the one-way clutchcomprising a first clutch portion and a second clutch portion, the firstclutch portion being mounted on the pivot shaft, the second clutchportion being rotatable about the pivot shaft, the one-way clutch beingconfigured to permit rotation of the second clutch portion relative tothe first clutch portion in the first rotational direction but resistrotation of the second clutch portion relative to the first clutchportion in a second rotational direction that is opposite the firstrotational direction, the second clutch portion being engaged to thepivot arm with a predetermined amount of rotational play that permitsthe pivot arm to be moved between a maximum tension position and aminimum tension position for a given positioning of the second clutchportion without affecting a position of the second clutch portionrelative to the pivot shaft.
 3. The tensioner of claim 2, wherein thedamper is coupled to at least one of the first and second clutchportions
 4. The tensioner of claim 3, wherein the one-way clutchinhibits rotation of the second clutch portion about the pivot shaft inthe second rotational direction when the pivot arm is subjected to apredetermined threshold torque.
 5. The tensioner of claim 3, wherein theone-way clutch comprises a wrap spring, the wrap spring being configuredto non-rotatably couple the first and second clutch portions based on adirection of motion input by the pivot arm to the second clutch portion.6. The tensioner of claim 5, wherein the one-way clutch comprises alimiter for limiting radial expansion of the wrap spring.
 7. Thetensioner of claim 3, wherein the one-way, clutch comprises a frictionclamp that is frictionally engaged to the pivot shaft.
 8. The tensionerof claim 7, wherein the friction clamp is deflectable when a torque inexcess of a predetermined torque is applied to the second clutch portionin the second rotational direction to thereby reduce friction betweenthe friction ring and the pivot shaft.
 9. The tensioner of claim 3,wherein the first and second clutch portions are snap-fit together. 10.The tensioner of claim 3, wherein one of the pivot arm and the secondclutch portion comprises a tongue, wherein the other one of the pivotarm and the second clutch portion comprises a slot into which the tongueis received and wherein the slot is larger than the tongue to permit apredetermined amount of relative movement between the pivot arm and thesecond clutch portion.
 11. The tensioner of claim 1, wherein the dampercomprises a plurality of lobes.
 12. The tensioner of claim 1, whereinthe damper has at least two spring rates, a first one of the springrates being associated with compression of the damper by an amount thatis less than or equal to a predetermined first amount, a second one ofthe spring rates being associated with compression of the damper by anamount that exceeds the first amount.
 13. The tensioner of claim 1,wherein the damper comprises an annular wall and a plurality of dampermembers that extend radially outwardly from the annular wall.
 14. Thetensioner of claim 13, wherein each of the damper members is coupled tothe annular wall by a single end member.
 15. A tensioner comprising: apivot shaft; a pivot arm pivotally mounted on the pivot shaft anddefining a groove; a torsion spring that biases the pivot arm about thepivot shaft in a first rotational direction, the torsion spring being aclosing-type torsion spring with a plurality of coils that are receivedabout the pivot shaft; a stop sleeve received over the pivot shaft andwithin the torsion spring, the stop sleeve having a tongue that isreceived into the groove in the pivot arm, the tongue being smaller thanthe groove to permit a predetermined amount of movement of the pivot armrelative to the stop sleeve; a first clamp sleeve mounted over the pivotshaft and rotatably coupled to the stop sleeve; a wrap spring having afirst end, which is fixedly coupled to the first clamp sleeve, and aplurality of helical coils that are disposed about the stop sleeve; asecond clamp sleeve mounted over the pivot shaft and abutting the firstclamp sleeve on a side opposite the stop sleeve, the second clamp sleevebeing non-rotatably coupled to the first clamp sleeve; at least onedamper coupled to the second clamp sleeve and configured to be incontinuous contact with an inside surface of the coils of the torsionspring, the at least one damper being formed of a resilient material anddeflecting inwardly with increasing torque transmitted through thetorsion spring; and a friction clamp housed between the first and secondclamp sleeves, the friction clamp frictionally engaging the pivot shaft.16. The tensioner of claim 15, wherein the first clamp sleeve isconfigured to maintain the friction clamp in a closed position aroundthe pivot shaft when the pivot arm is moved in the first rotationaldirection and wherein the first clamp sleeve is configured to permit thefriction clamp to spread open when a torque in excess of a predeterminedtorque is applied to the pivot arm in a second rotational directionopposite the first rotational direction.
 17. The tensioner of claim 15,wherein the at least one damper comprises a plurality of lobes that aredisposed about the second clamp sleeve.
 18. The tensioner of claim 17,wherein each of the lobes is supported on its opposite sides by a wallmember.
 19. The tensioner of claim 15, wherein the at least one dampercomprises an annular wall and a plurality of damper members that extendradially outwardly from the annular wall.
 20. The tensioner of claim 19,wherein each damper member is coupled to the annular wall by a singlewall member.
 21. The tensioner of claim 15, wherein the stop sleeve andthe second clamp sleeve are snap-fit to the first clamp sleeve.
 22. Atensioner comprising: a pivot shaft; a pivot arm pivotally mounted onthe pivot shaft and defining a groove; a torsion spring that biases thepivot arm about the pivot shaft in a first rotational direction, thetorsion spring being a closing-type torsion spring with a plurality ofcoils that are received about the pivot shaft; a pulley mounted on thepivot arm at a location that is offset from the pivot shaft; a stopsleeve received over the pivot shaft and within the torsion spring, thestop sleeve having a tongue that is received into the groove in thepivot arm, the tongue being smaller than the groove to permit apredetermined amount of movement of the pivot arm relative to the stopsleeve; a first clamp sleeve mounted over the pivot shaft and rotatablycoupled to the stop sleeve; a wrap spring having a first end, which isfixedly coupled to the first clamp sleeve, and a plurality of helicalcoils that are disposed about the stop sleeve; a second clamp sleevemounted over the pivot shaft and abutting the first clamp sleeve on aside opposite the stop sleeve, the second clamp sleeve beingnon-rotatably coupled to the first clamp sleeve; at least one dampercoupled to the second clamp sleeve and configured to be in continuouscontact with an inside surface of the coils of the torsion spring, theat least one damper being formed of a resilient material and deflectinginwardly with increasing torque transmitted through the torsion spring;and a friction clamp housed between the first and second clamp sleeves,the friction clamp frictionally engaging the pivot shaft; wherein thefirst clamp sleeve is configured to maintain the friction clamp in aclosed position around the pivot shaft when the pivot arm is moved inthe first rotational direction and wherein the first clamp sleeve isconfigured to permit the friction clamp to spread open when a torque inexcess of a predetermined torque is applied to the pivot arm in a secondrotational direction opposite the first rotational direction; whereinthe at least one damper comprises a plurality of lobes that are disposedabout the second clamp sleeve; wherein each of the lobes is supported onits opposite sides by a wall member; and wherein the stop sleeve and thesecond clamp sleeve are snap-fit to the first clamp sleeve